1. Field of The Invention
The present invention relates generally to an infrared radiation sensor for measuring the temperature of a subject, such as a tympanic membrane, without contact therewith. More specifically, the invention relates to an infrared radiation sensor having a bridge structure on which a thermally sensitive portion is formed.
2. Description of The Background Art
In thermal type infrared radiation sensors, the temperature of a substance is measured on the basis of the temperature increase of a thermally sensitive portion which is heated by infrared radiation radiated from the substance. Various technologies for making the sensors compact and highly-sensitive have been proposed. In particular, when the temperature of a substance is substantially equal to or less than room temperature, the amount of infrared radiation received by the sensor is very small. Therefore, it is necessary to decrease the heat capacity of the sensor and to prevent the energy of the received infrared radiation from being scattered and lost as much as possible.
In recent years, various infrared radiation sensors reduced in size to decrease their heat capacity and having a bridge structure to prevent heat from being scattered and lost due to conduction of heat, have been proposed (JP-A 57-178149, 62-277528 and JP-A 3-136379). These sensors are designed to decrease heat capacity by compacting using semiconductor fine patterning or micromachining, and they have a thermally sensitive portion on a bridge structure which does not make contact with a substrate in order to prevent heat from being scattered and lost due to conduction of heat.
The infrared radiation sensors disclosed in JP-A 57-178149 and JP-A 62-277528 are obtained by forming on a silicon substrate or a metallic substrate an insulating film of a laminated film consisting of a silicon oxide film (SiOx) and a silicon nitride film (SiNy), transcribing a pattern of a bridge portion on the insulating film by a photolithographic technique, forming and patterning a predetermined wiring and thermally sensitive portion on the insulating film which has not been etched, and selectively etching a part of the substrate to form a caved portion. These methods are referred to as "anisotropic etching" or "isotropic etching" in accordance with a manner for selectively etching a part of the substrate.
The infrared radiation sensor disclosed in JP-A 3-136379 is obtained by accurately forming a caved portion which is to be arranged below a bridge portion, on a substrate at a predetermined region prior to the formation of the bridge portion; filling in the caved portion with a metallic film which serves as a sacrificial layer for forming the bridge portion, to make the surface of the substrate even; forming on the whole even surface an insulating film of laminated film of a silicon oxide film and a silicon nitride film, or an insulating film of an organic material; forming a pattern of a bridge on the insulating film by photolithography and etching; patterning metallic wirings and a thermally sensitive portion; and selectively etching only the sacrificed layer.
However, since these conventional infrared radiation sensors are provided to improve the yield of t he formation of a bridge portion, the dimensional accuracy thereof, the uniformity of thermal characteristics of each sensor element and the accuracy of temperature measurement, they are not designed to increase the amount of received infrared radiation to improve the sensitivity of the sensor.
For that reason, these infrared radiation sensors can not achieve fully high-sensitive measurement of temperature since the shape of the bridge portion is not designed to be optimized in view of the amount of received infrared radiation energy and the amount of energy lost due to heat conduction of the bridge portion in order to increase the temperature increase of the thermally sensitive portion on the bridge portion.